The present disclosure relates generally to a radiopaque material and, more particularly, to processes for inspecting components.
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a compressor section to pressurize an airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases.
Gas turbine engine hot section components such as blades and vanes are subject to high thermal loads for prolonged time periods. Other components also experience high thermal loads such as combustor, exhaust liner, blade outer air seal, and nozzle components. Historically, such components have implemented various air-cooling arrangements that permit the passage of air to facilitate cooling. In addition, the components are typically provided with various coatings such as thermal barrier coatings to further resist the thermal loads.
The internal passage architecture may be produced through various processes such as investment cast, die cast, drill, Electron Discharge Machining (“EDM”), milling, welding, additive manufacturing, etc. Investment casting is a commonly used technique for forming metallic components having complex geometries, especially hollow components, and is used in the fabrication of superalloy gas turbine engine components.
A ceramic core is typically used in the manufacturing process to form the hollow internal cavities therein. Oftentimes, manufacture, repair, and/or remanufacture, requires formation of an internal cavity and/or protection thereof from harsh chemicals to prevent internal surfaces from being coated, and/or to facilitate non-destructive testing techniques. Various processes may require temperatures that may be near the alloy incipient melting point as well as utilize reactive chemicals which may limit the choice of fill materials.
The core may be leached out of the component by dissolution or other reactive erosion method subsequent to manufacture, repair, and/or remanufacture. Single-crystal superalloy casting is typically leached of an alumina or silica-base ceramic core by flushing with a caustic solution. This leaching process may not always be successful in the complete removal of the core, which may affect the function of the final component through distortion of the internal passage architecture. As such, the component is typically inspected via a neutron radiography (“N-ray”), where neutrons are utilized to substantially penetrate the metal casting but are more attenuated by tagging agents that bind to residual core material that remain within the internal passage architecture after the leaching process. This N-ray process, although effective, is relatively expensive and complex as a nuclear reactor or particle accelerator is required to produce a sufficient neutron source.